THE TECHNICS OF CASEIN PAINTING. 69 



To facilitate the fresco painting the upper layer of plaster 

 can be put on in sections, or else kept soft for a considerable 

 time by wetting it with water that has been boiled, or by 

 hanging wet cloths over the surface. This prevents the too 

 rapid crystallisation of the lime, which would otherwise occur. 



Dry fresco painting is performed in the following manner. 

 Old or dry plaster walls are scrubbed with a stone until the 

 upper surface has been worn away and the sound absorbent 

 plaster is reached; but if the crust is sound and rough 

 grained it need not be removed. A mixture of fluid casein 

 medium, white outdoor cement and 10 per cent, of calcined 

 magnesia is then mixed and diluted with previously boiled 

 and cooled water, the first coating being thinner than the 

 others ; and, the wall having been damped with recooled or 

 rain water, several coatings of this mixture are applied in 

 succession. As soon as the surface has dried dull, several 

 coatings of ground colour are laid on, and the decorations 

 and painting are then applied. 



According to Martin, the aforesaid out-door cement is 

 also known as "white Portland cement," and is prepared by 

 mixing 1 per cent, of iron-free kaolin, 3 to 5 parts of pure 

 white chalk, followed by 2 to 5 per cent, of gypsum or 3 to 

 5 per cent, of magnesium chloride. The ingredients, wet or 

 dry mixed, are calcined in an oven. 



Probably the best method of imitating the old Pompeian 

 wall paintings in character and durability is the dry fresco 

 process of Gerhardt. In some cases, however, it is possible 

 to dispense with scouring the walls beforehand, replacing this 

 treatment by the less troublesome process of soaking the 

 walls several times over with paint soap at the completion 

 of the work, this treatment increasing the brightness of the 

 colours and improving their character and durability. 



After the impregnated surface has dried it may be polished 

 to a dull gloss with a brush. The precautions specified must, 



